stress-sigsegv: Fix typo, __NetNBSD__ -> __NetBSD__

Fix NetBSD build check for address space sizing.
Fixes: commit 7288c64 ("stress-sigsegv: stress-sigsegv: set max mask shift of 46 bits for NetBSD and OpenBSD")

Signed-off-by: Colin Ian King <colin.i.king@gmail.com>

Author: ColinIanKing

stress-sigsegv.c

@@ -61,7 +61,7 @@ static volatile int code;
 #endif
 
 #if defined(__FreeBSD__) ||	\
-    defined(__NetNBSD__) ||	\
+    defined(__NetBSD__) ||	\
     defined(__OpenBSD__) ||	\
     defined(__sun__)
 #define MAX_MASK_SHIFT	(46)